The present invention relates to an apparatus for producing pure water, and, more particularly, to an apparatus suitable for pharmaceutical and semiconductor industries.
Water of high purity is required in the pharmaceutical industry for manufacturing drugs and medicines as well as in the electronic industry for manufacturing semiconductor devices. For instance, in the manufacture of minute semiconductor devices, such as integrated circuits (I.C.) or large scale integrated circuits (L.S.I.), the purity of washing water is directly related to the quality of the products. Accordingly, the high purification of water is of great concern.
In a conventional pure water producing apparatus, raw water is fed through a raw water supply line into a first intermediate tank for temporary storage. Then the raw water is supplied by a high pressure pump to a reverse osmotic or semipermeable membrane in a reverse osmotic unit at a pressure above the osmotic pressure for removing salt. Permeated water which has been desalted by the reverse osmotic unit flows through a permeated water line and is stored into a second intermediate tank having a free liquid level. The permeated water is stored not only to prevent the semipermeable membrane in the reverse osmotic unit from being damaged due to a closed operation, but also to purge the free liquid level with an inert gas such as nitrogen, thereby maintaining desirable qualities of water. Concentrated water produced in the reverse osmotic unit is discharged therefrom through a concentrated water line. The permeated water in the second intermediate tank is forced by a pure water pump to flow through a purifying equipment which comprises a polisher, an ultraviolet sterilizer, a filter or the like, and thence the water so treated is fed to a use point where it is consumed as washing water. Unused treated pure water is returned to the second intermediate tank through a circulating line. By the circulating line, the unused pure water is successively circulated through the second intermediate tank, the purifying equipment, and the use point for preventing degradation of water. According to such a conventional apparatus, water can be degraded due to the existence of two intermediate tanks. For instance, if a small amount of bacteria would leak in such tanks, they would proliferate resulting in a contamination of the inside of the tanks by a huge amount of bacteria. Since the reverse osmotic unit is out of operation while pure water is being unused in the use point, the semipermeable membrane is subjected to an intensive contamination. The semipermeable membrane thus contaminated must be washed frequently. To wash the semipermeable membrane, a washing liquid tank and a washing liquid pump are disposed out of the main treatment line for circulating a washing liquid through the semipermeable membrane.
The foregoing apparatus is described in MEMBRANE APPLICATION TECHNOLOGY HANDBOOK, published by Saiwai Shobo on July 15, 1983, P191 "Reverse Osmotic Membrane, Ultrafiltration II, Application".
An object of the present invention is to provide an apparatus for producing pure water which eliminates the need for intermediate tanks which would otherwise degrade pure water, thereby preventing degradation of pure water due to stagnation thereof.
According to the present invention, an apparatus for producing pure water from raw water, comprises a reverse osmotic membrane unit, a polisher, an ultraviolet sterilizer, a high pressure pump for forcing raw water to flow through a reverse osmotic membrane in reverse osmotic membrane unit to produce pure water permeated therethrough, and for feeding pure water to a use point, or consumer and a circulating line extending between the use point or consumer and a suction side of the high pressure pump for circulating pure water therebetween, whereby a technical measure for preventing degradation of pure water caused by stagnation is realized.